Mucosal epithelia are the first tissue sites of contact of HIV with the human body during the course of infection, and these play a critical role in determining its success in establishing systemic infection. We have also shown that the efficiency of transcytotic penetration by HIV varies with the degree of stratification of the mucosal epithelium, as well as with the levels of expression of the anti-HIV innate proteins beta-defensin 2 and 3, and secretory leukocyte protease inhibitor (SLPI). We have shown that HIV transmission through mucosal epithelial cells can occur by transcytotic and between epithelial cells by transsynaptic penetration. Spread from epithelial cells to immune cells by transsynaptic transmission may then lead to systemic HIV infection. Transmission through adult mucosal epithelium such as that of the cervix, and across fetal/neonatal oral or intestinal epithelium remain important clinical problems. There are currently no vaccines available to reduce HIV transmission and other preventive approaches such as administering antiretroviral therapy to exposed individuals may not work since neither transcytosis nor transsynaptic transmission require viral replication or fusion of viral membranes with cellular membranes. New methods to reduce HIV transmission across mucosal epithelia are urgently needed, but to develop these methods, a better understanding of the molecular mechanisms of HIV transcytotic and transsynaptic transmission across epithelial surfaces is critical. Accordingly, the specific aims of this proposal are: (1) To determine the mechanisms of transcytotic and transsynaptic spread of HIV through mucosal epithelia;(2) To determine the role of epithelial anti-HIV innate proteins in HIV transmission across mucosal epithelia. The data obtained from this proposal will greatly advance current knowledge about the mechanisms of HV transmission across mucosal epithelia and will open new avenues for designing drugs that may specifically block HIV passage across these epithelia. PUBLIC HEALTH RELEVANCE: HIV transmission via mucosal epithelium is one of the key initial steps in establishing HIV infection but this process remains poorly understood. This study will characterize the different ways used by HIV to pass through epithelium to infect immune cells, and the various defenses used by epithelial cells to inactivate HIV. Knowledge obtained from these studies may lead to the development of new approaches to prevent HIV infection.